Availability heuristic consists on the act of making a decision based loosely on previous experience, without taking into consideration the entire extent of what the previous experience entailed, nor many other details that may actually render the experience null as a main motivator for choice-making. In not so many words, it is making a decision just because of the assumption that things will go right, or wrong, because in a previous time that was the way things went.
The cognitive benefit of availability heuristic is that, at least it entails the process of retrieving data from long term memory. Although this data is not retrieved in its entirety (only bits and most salient pieces of it), it is better to do this than to make a choice on the spot without considering any previous experiences at all. Doing this, would mean that somewhere in our cognitive processes there is no correlations regarding acts and their consequences. Hence, processing the memories in order to make a choice is indeed a good behavior pattern when problem solving this way. It is activating schema.
The problem with relying on availability heuristic depends on what choice we are going to make. For instance, if a woman chooses never to speak to males again because she had a negative previous experience involving a man, she is limiting her social and emotional choices to a high extent. Moreover, she is not taking into consideration the many other factors involved in one single experience. Often when we think about something that happened to us we retrieve either a very happy or a very sad occasion as part of our internal motivation processes to make choices. Hence, it is mainly an emotional, and not an analytical choice, what we end up making. Therefore, to avoid this there must be a lot of objectivity in the retrieval of long term memories. The best solution is to consult with a counseling professional that is able to take every detail into consideration and analyze it with equal weight placed upon each detail.